Undesired and/or uncontrolled algal bloom is a constant problem in bodies of water such as swimming pools, aquaculture ponds, freshwater ponds, aquariums, urban drainage systems, industrial cooling water systems and even in the vast ocean. Such algal blooms, if left unchecked, can multiply to the point of rendering the water unfit for human use. For example, filamentous algae, or commonly referred to as “pond scum” or “pond moss” forms greenish mats upon the water's surface. The stringy, fast-growing algae can cover a pond with slimy, lime-green clumps or mats in a short period of time. Some common types of problematic filamentous algae are of the genera Spirogyra, Cladophora and Pithophora. Algal blooms of the toxic algae such as dinoflagellates of the genus Alexandrium and Karenia occur worldwide on a regular basis and threatening people's access to food (e.g., fish and shellfishes) and their livelihoods. These toxic algae produce potent toxins given the right conditions. Algal blooms can cause harm through the production of toxins or by their accumulated biomass, which can affect co-occurring organisms, e.g., fishes that feed on them, and alter food-web dynamics. Impacts include human illness and mortality following consumption of or indirect exposure to the harmful algal bloom toxins, substantial economic losses to coastal communities and commercial fisheries, and algal bloom-associated fish, bird and mammal mortalities. To the human eye, such blooms can appear greenish, brown, and even reddish-orange depending upon the algal species, the aquatic ecosystem, and the concentration of the organisms. When the bloom takes on a red or brown hue, it is known colloquially as a red tide.
Various strategies have been used to control algal blooms. Early attempts to solve this problem have included the use of active chlorine, copper-containing compounds or quaternary ammonium salts. Natural algicides (or “algaecides”) such as barley straws are also used. In England, barley straws are placed in mesh bags and floated in fish ponds or water gardens to help reduce algal growth without harming pond plants and animals. Herbicides are used on a regular basis to control any unwanted aquatic vegetation and to prevent fouling of aquaculture cages. However, this has led to the development of herbicide resistant algae, e.g., Pithophora. Synthetic algicides include copper sulphate, chromate-based compounds and n-alkyl-dimethyl benzyl ammonium chloride (e.g., Polyquat and Clorox) which are very toxic and environmentally hazardous. Active chlorine-containing compounds also have other serious drawbacks including rapid decomposition, pungent odor and corrosive action of water handling systems.
Copper compounds, such as copper sulfate, copper carbonate and other related copper salts tend to exert algaecidic activity only at relatively high concentrations making use of such compounds expensive. Copper salts, such as copper sulfate, also have a tendency to precipitate from aqueous solutions containing carbonates and bicarbonates. U.S. Pat. No. 2,734,028 to Domogalla attempts to solve this problem of copper precipitation by the inclusion of an hydroxyamine, such as alkanolamine, as a solubilizing agent to maintain the copper cation in solution in a variety of hard water systems or in water having large amounts of dissolved carbon dioxide.
Quaternary ammonium compounds have also been proposed as algaecides and bactericides. Their bactericidal power has been attributed to the tensio-active effect and the formation of compounds between quaternary ammonium salts and proteins. These compounds, however, have been known to irritate human skin and to loose activity in the presence of hard, calcium-containing water. Stayner et al., U.S. Pat. No. 2,692,231, indicate that quaternary ammonium salts, such as alkyl dimethyl benzyl ammonium chlorides by themselves are inadequate under certain circumstances. Their attempted solution is to combine the quaternary ammonium salt with a nonanionic organic material having a water solubility of less than about 5%. The nonanionic organic material is characterized as being hydrophobic-weakly hydrophilic species and as a promoter for the quaternary ammonium salt enhancing the microbicidal effect of the quaternary ammonium compound.
Darragh et al., U.S. Pat. No. 2,688,583, disclose that quaternary ammonium salts have the further drawback of producing a cloudy dispersion upon being added to water. Their solution to this problem is to include with the quaternary ammonium salt an inorganic water soluble aluminum salt capable of producing clear aqueous dispersions throughout a range of concentrations. Aluminum sulfate or aluminum chloride has been employed in this capacity.
Zsoldos et al., U.S. Pat. No. 3,702,298, have attempted to control the growth of micro-organisms in water by maintaining a highly oxidizing alkaline aqueous solution consisting of an oxidizer bank of a large excess of peroxy compounds in combination with copper or silver salts (such as nitrate or sulfate salts) acting as an in situ catalyst. Optionally, a chelating agent, such as sodium citrate or acetate, can be employed to prevent precipitation of the metal catalyst.